How Long Will My Money Last?

How this calculator works

Each monthly withdrawal is taken before that month's investment growth. Spending increases at the start of each subsequent year. The result counts fully funded monthly withdrawals and reports the first shortfall within your selected horizon.

Requested withdrawal in month k = annual spending / 12 x (1 + inflation)^floor((k - 1) / 12). Balance = max(0, balance - withdrawal) x (1 + monthly net return).

Rates in formulas are decimals. P is starting savings, C is the monthly contribution, n is the number of months, and m is the effective monthly return. Net annual growth is (1 + gross return) × (1 - annual fee) - 1. The equivalent monthly rate is (1 + annual rate)^(1/12) - 1. Real returns also divide the annual growth factor by (1 + inflation).

Example: At zero return, fees and inflation, 120,000 can fund 1,000 per month for 120 months, or 10 years. The next monthly withdrawal would have a shortfall.

Change the examples to reflect your situation and test less favorable assumptions. These simplified formulas exclude country-specific taxes and benefits. Constant investment returns do not capture market volatility or the order in which gains and losses occur.

Common questions

Background & references

These references explain the underlying concepts. The formulas and timing described above define this tool; no country-specific rules are imported from the references.

• Charles Schwab: the 4% rule and its limitations
• Investor.gov: purchasing power